Patent Document 1 discloses a direct injection engine having an outwardly-opening fuel injection valve arranged on the center axis of a cylinder, and injecting a fuel in the shape of a hollow cone. In this direct injection engine, the fuel is injected into the cylinder in the last stage of a compression stroke, thereby forming, in a combustion chamber, an air-fuel mixture layer and a gas layer around the air-fuel mixture layer. The engine disclosed in Patent Document 1 reduces the cooling loss by making the gas layer surrounding the air-fuel mixture serve as a heat-insulating layer during the combustion of the air-fuel mixture.
Patent Document 2 discloses a compression self-ignition engine in which a wall surface dividing a combustion chamber is made of a heat-insulating material to reduce cooling loss by the wall surface of the combustion chamber.